1. Field of the Invention
The present invention relates to a laser induced liquid jet generating device that generates a jet stream by irradiating liquid with a laser beam.
2. Description of the Related Art
As a way of treating thrombosis, i.e., a condition in which human blood vessels are obstructed, a treatment method of physically pulverizing matter causing thrombosis with a liquid jet stream has been discovered in recent years. This treatment method is highly appreciated as a very promising treatment method for thrombosis as it is not necessary to administer thrombolytic agents in large quantities which can cause serious adverse effects such as bleeding. Also an earlier resumption of blood flow is possible compared to a case of using thrombolytic agents only. In particular, while it is believed that the accompanying nerve symptom becomes difficult to be improved if an ischemic condition lasts for more than six hours, an extremely high recovery effect can be expected if the resumption of blood flow occurs within a few hours of the crisis.
Unexamined Publication No. JP-A-2003-111766 (refer to sections 0014, 0015, and FIG. 1), Unexamined Publication No. JP-2002-521084 corresponding WO00/04838 (refer to sections 0004, 0010, 0096, and FIG. 27), and JJSLM (THE JOURNAL OF JAPAN SOCIETY FOR LASER SURGERY AND MEDICINE) No. 3, Vo. 22 (2001) (refer to p. 217) disclose a method of introducing a pulsing laser beam from a laser oscillator into an optical fiber inserted into a catheter in order to rapidly heat physiological saline solution that fills said catheter, induce a liquid jet stream, thus to crush and remove thrombi and the like with the force of the liquid jet stream.
In this method, a catheter in which an optical fiber is inserted, is brought to the vicinity of a thrombus before a liquid jet stream is generated in order to intensify the treatment effect by minimizing the depreciation of the force of the liquid jet stream.
A traditional catheter is a long, small diameter tube made of such materials as polypropylene and polyimide, generally flexible in order to be able to deform easily in accordance with winding blood vessels and tends to absorb the laser beam easily as described in Unexamined Publication No. JP-A-2002-521084 (WO00/04838), so that it tends to be affected thermally when it is subjected to intense laser beams.
When an optical fiber with an outside diameter (core diameter) of approximately 0.4 mm is inserted into a flexible catheter made of such a material with a small diameter (normally 0.9 mm), it is common that only an extremely small clearance exists between the inner surface of the catheter and the outer surface of the optical fiber. If a strong laser beam irradiation is applied under this condition, the heat of the laser beam is transmitted to the catheter, and the laser beam's energy is absorbed by the catheter's material to cause melting or deformation of the catheter. This may hinder the liquid jet stream from being ejected smoothly and shorten the life of the catheter itself. There is also a concern that the heat that melts or deforms resins or metals may affect blood vessels as well.
For these reasons, it has also been considered that the area for generating a strong liquid jet stream by an irradiating laser beam should not be located inside of the catheter which is inserted into a blood vessel, but rather should be located on the outside of the proximal part of the catheter, i.e., outside of the catheter. However, it is necessary in that case to use a laser irradiation of a higher power to generate a liquid jet stream of the same strength as the aforementioned method because the distance from the laser irradiation part to the catheter tip becomes longer than the aforementioned method. As a consequence, the vicinity of the laser irradiation part becomes substantially hot. Patients and operators who accidentally touch the laser irradiation part that has turned very hot can get burned. A high power laser beam and the high temperature caused by it can expedite the deterioration of the material in the neighborhood of the laser irradiation part, eventually damaging the device. Moreover, if a drug solution containing a drug such as thrombi solvent is used as the liquid to be irradiated with a laser beam to generate a jet stream, the high heat generated as a result of the laser irradiation may reduce or eliminate the efficacy of the drug in the drug solution.
Consequently, problems have arisen in minimizing how to minimize the effect of the heat generated by the laser irradiation on the outside of the catheter.